Valve commutator and its use in multiplex signaling



Dec. 8, 1931.

J. S. STONE VALVE 4GOMMUTA'IOR AND lTS USE IN MULTIPLEX SIGNALING -FledDeo.

6 Sheets-Sheen:- 1

` ATTORNEY J. s. STONE 1,835,099

VALVE GOMMUTATOR AND ITS USE vIN MULTIPLEX SIGNALING Dec.Y s, 1931.

Filed Dec. 28,v 1929 6 Sheets-Sheet 2 lNvENToR v 707mm 152012@ Sta/@e BYATTORNEY VII Dec. 8, 1931. 5 gul-ONE 1,835,99

VALVE GOMMUTATOR AND ITS USE IN MULTIPLEX SIGNALING lFiled Dec. 28, 19296 Sheets-Sheet 5 TTORNEY J. S. STONE Dec. s, 1931.

'VALVE COMMUTATR AND ITS USE INKMULTPLEX SIGNALING Filed Do.

28, 1929 e sheets-smet l1 nNvx-:NTOR Jz@ Sw/ae Stan/e ATTORNEY J. S.STONE Dec. s; 1931.

VALVEVCOMMUTATOR AND ITS USE-IN MULTIPLEX SIGNALING 6 Sheets-Sheet 5Filed Dec:` 28, 1929 foo, 00o

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fao t m50 E M2 E 3 INVENTOR YJo/fu@ 3 010e Stone ATTORN EY J. s. STONEy1 1,835,099 VAL VE COMMTATOR AND ITS USE IN MULTIPLEX SIGNALING FiledDeC. 28, 1929 E, sr, abt

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ATTORNEY Patented Dec. 8, 1931 UNITED 'STATES PATENT-*cruce .i

JOHN STONE STONE, 0F SAN DIEGO, CALIFORNIA, ASSIGNOR T0. TELEPHONE vANDTELEGRAPH COMPANY, A CORPORATION 0F NEW YORK VALVE-GOMMUTATOR AND ITSUSE IN SIGNALING Application filed December 28,119.29. Serial No.417,168.

An object of my invention is to provide a new and improved commutatorfor periodically changing the effective connections of elect-riccircuits. Another object of my invention is to provide a commutatorcomprising a vacuum discharge tube in Vwhich the transmission of currentis determined by theV application of a superposed locally generatedelectroinotive force. Another object of my invention is to provide formultiplex signaling by the aid of my improved commutators. These objectsand other objects of my invention will become apparent on considerationof a limited number of specific embodiments of the invention which Ihave chosen to illustrate and describe in this specification. It will beunderstood that the following description relates to these particularexamples of the practice of my invention and that the invention will bedefined in the appended claims.

Referring to the drawings, Figure 1 is a diagram showing a combinationby means of which certain fundamental principles of the invention may beexplained. Fig. 2 is a diagram showing certain impedance components andtheir resultant for Fig. 1 as functions of the adjustable or variableresistance R1.

. Fig. 3 is a diagram showing resistance as a function of a certainphase angle for an ordinary thermionic vacuum tube r which may take theplaceof the resistance R1 in Fig. 1. Fig. l is a diagram of impedance asa function of phase angle when the vacuum tube Fig. 1 as dependent onsource'el.

referred to takes theplace of the resistance R1, and an alternatingelectromotive force is applied as at el. Figs. 5 and 5a are diagramsshowing the resistance of the element 1' of Figs. 6 to 11 are furtherdiagrams extending the scope and application of the principles`exhibited in connection with Figs. 1 to 5. Figs. 123and 13 are diagramsshowing impedance and current for Fig. 1 as dependent on the source el'.Figs. 14 to 25 illustrate furthermodiiications in the application of theprinciple of my invcntion. Figs. 26 and 27 are diagrams showing how theinvention may be employed in the practice of `multiplex signaling.I Fig.28 shows how `the invention may be employed to a condenser .ofcapacityC, and in shunt to the condenser a resistance R1, which isadjustable or'variable in value.

Let the resonant frequency of the coil and condenser be 'wo/2W so thatCZw02=1.

At the Afrequency 10o/2W, let the impedance of the network between 101,102 in Fig. 1 be represented by Zand the "component resistance by R andthe componentreactance by X. vThen the following relations are easilyestablished: l j

I i R1 R R+-m (l) Z1= WW (3) These functional relations are exhibitedrespectively in the curves 1, 2 and 3 of Fig. 2, in which forconvenience the axis of abscissae is marked in units of value of Rl/L'w0and the axis of ordinates in units of Lwo. Further, in the diagram ofFig. 2 the ratio Lwo/R is taken as 100.

As lillustrated by curve 3 of Fig. 2 and as may be deduced fromEquations 1, 2 and 3, when the shunt resistance R1 takesthe low value ofLeva/8 the impedance of the network is 99.4% lof its maximum impedanceLwo, which is the value the network impedance attains when theresistance R1 reaches zero value. n

The symbol designated by 7 in Fig. 1 represents a thermionic vacuum tubeof two electrodes, a valve which passes current only one way. In such adevice the current il is related to the impressed voltage elapproximately according to the equation z'lsae, for positive values ofel; for negative values of el the current, l is zero. Let the impressed'voltage be sinusoidal so that 61:1?, sin wlt where El is the maximumvoltage, as shown in Fig. 5; let this be fixed in value by the equationaE1=8/Dwo.

For the purpose of the present discussion let the resistance of thetwo-electrode vacuum tube be defined as the ratio of the appliedelectromotive force to the current and let this resistance berepresented by the character r; accordingly r=e1/'1=c1/ae12=1/ael. (Whenthe resistance is defined as the ratio of the increment of appliedelectromotive force to the increment of corresponding current, itresults that r=del/clzl=1/2ae1, showing that the definition here adoptedgives a value having a constant relation to the value given by thisother definition; that is the definition here adopted gives a valuedouble that of the other definition.) From the definition here adoptedand from the immediately foregoing equations, the diagram of Fig. 3 maybe deduced, showing the resistance as a function of the argument angleaccording to the equation 1 Lw0 T l/ael nMEI sin wit-8 sin wlt (3a) Fromthe curve of Fig. 3 it will readily be seen that the resistance of thevalve remains less than Lw., when wl lies between 7 and 173o for eachhalf cycle of impressed electromotive force. This is also shown in thefull line curves of Fig. 50;.

Now let the switches S in Fig. 1 be shifted, thus substituting the valveR and associated elements for the resistance R1. From Figs. 2 and 3 andthe corresponding equations, the impedance Z (at frequency lw1/27r)"ofthe network of Fig. 1 may be obtained as a function of the phase anglefor the source el. The result is the curve of Fig. 4.; also see the fullline curve of Fig. 12. These curves show the instantaneous values of theimpedance Z of the network of Fig. 1 across 101, 102 as the resistanceof the valve r in shunt to the condenser C varies cyclically as shown inFig. 5a, due to the varying electromotive force El sin w12? of sourceel. Tt will be noted that the impedance of the network rises veryrapidly from lwlzf=0 to wlt=10O and that it remains practically constantfrom 200 to 1600 over which range the impedance is substantially thevalue Lwo.

It is to be understood that the assumed frequency f1/2W is extremelysmall compared to the frequency @v0/2r of the resonant circuit L, G. Forexample, the former frequency may be taken at about 125 and the latterat 62,500 or more. Thus the steady state values of the apparentresistance R, apparent reactance X and the impedance Z of the networkare properly taken without danger of committing any appreciable errorthereby.

The full line curve of Fig. 12 gives the impedance of the network ofFig. 1 to currents of frequency wu/2W, over a range of two cycles of thevarying shunt valve resistance r as determined by the electromotiveforce eL of frequency ufl/2W.

Referring to Fig. 1, the amplitude El of the source el is assumed to begreat compared to the amplitude E., of the force of frequency coo/211-applied to the terminals 101 and 102. The impedanccs 103, 104- aslindicated in Fig. 1, are negligible for the electromotive force elhaving the relatively low frequency w1/2r, but they are high for theforce applied to terminals 101, 102, which has the relatively highfrequency @0o/21T.

The mode of operation of the system 1 is shown by Figs. 12 and 13. From0O to 180O the electromotive force from the source el is applied to thevalve r in the direction to pass current, and over most of the rangereferred to the valve fr is caused to have a low resistance as shown inFig. 5a. When the rcsistance of the valve r is low, the impedance of thenetwork across the terminals 101, 102 is high and this high impedance isshown by the full line curve of Fig. 12. This high limpedance results ina low current value at the frequency coo/2T.- from 0O to 180o as shownin Fig. 13.

But when the electromotive force from the source el is applied in theopposite direction, as is the case from 1800 to 360, the valve r passesno current whatever, and its impedance is practically infinite. Thisvirtual open circuiting of the shunt around the condenser C causes theimpedance across the terminals 101, 102 at the resonant frequency w0/21rto hecome a minimum as shown in Fig. 12. Accordingly, the current acrossthe points 101, 102 becomes a maximum from 180o to 360" as shown in Fig.13.

It will often be desirable to employ the additional unidirectionalelectromotive force V in series with el, as by throwing the switch S inFig. 1. This will give a bias, having the effect to shift the axis ofabscissae up to 105 or down to 106 as indicated in dotted lines in Fig.The resulting change Iin the resistance of the valve R is shown by thedotted lines in Fig. 5a and the change in the impedance and currentacross the points 101, 102 is shown by the dotted lines in Figs. 12 and13. By giving a proper value to the electromotive force of V, thecurrent curve of Fig. 13 can be adjusted to make the open and closedcommutation periods approximately equal in duration as indicated by thedotted lines at- 107 and 108.

Fig. 6 shows a modification in which the inductance coil L is shunted bythe valve r and associated elements. With the arrangement shown in Fig.6 the current across 101, 102 at the frequency for which L and C areresonant is passed or blocked according to the phase of the generatorel. It will not be necessary to go into the theory in detail messagebecause` it corresponds: closely tothe theory for Fig. 1.

Fig. 7 illustrates a modification cofre sponding to Fig. 1 in Which twovalves r and r areV used', the object bein-g to equalize the load on thegenerator e1 over both half cycles, of its operation.

In the arrangement of Fig. 8 there are two inter-related networks, onebetween the pair ofterminals 101 and 102, the other between 101 and102', The system of Fig., 1 is duplicated in Fig.8 in such a Way thatVWhen 101,l 102 is open, then 101, 102 is closed, and vice versa.

.The modification of Fig.. 9 may be compared With that of Fig. 1. Fig.l9 is adapted for a case in Which the reactance Lw., of the coil L needsto be of relatively low value because of low electromotive force/acrossthe 2' points 101,102. The high frequency transformer T is employed andthe auxiliary condenser Cp is introduced to reduce the apparentreactanceof its pri-mary P to Zero. The apparent resistance across theterminals or" the primary P of the transformer T is given by theequation and the apparent reactance is given by the equation V Where r1is the ohmc resistance of P, r2 is the ohmic resistance of the secondarycoil VS,V.101 is the combined reactance of P and the condenser Cp, 62Vis the reactanceof the secondary circuit ot the transformer T, and m12is the mutual reactance of the transformer coils. The condition that,azl shall bezero is determined by equating this expression torwl to zeroand is Y This equation is satisfied giving the proper' value tothecorulenserA D, whereuponthe apparent resistanceV acrossl the primaryterminals oi' T becomesr"1v=r1.+ EL r2 Q7); $2.

of Fig.` 141 is open-circuited the impedance of the branch L1, Cl isreduced to the negligible resistance R1 'and the impedance of the branchL, C Will be effectively the reactance Lwo. On thel other hand, when thevalve 1 of Fig. 1% reaches its lowest resistance, the eiectiveresistance yof the branch L, C is L2w2 1R12 -I- 9012 Lwa (Lm, 21H1) andits effective reaotance is 2 Where r isthe lowest resistance of thevalve r. y Let, r2 be negligible compared `to L12w02, so that X"1=L1fw0(18) Y also let R1 be negligible compared to a", and r2 be negligiblecompared to 13121002. Ve then have in effect, Rlz negligible comparedto- :1f/12. Then:

R :R -lr and and

w 1 e 21E/L1 If Ll of Fig. 14 be made sufficiently large compared to L,then X may be made as small as desired and R may be made as nearly equalto R as we may require.

The principle here discussed in connecn tion with Fig. 14 may beextended as shown in F-ig. 15. In this diagram R1 and R2 are negligibleresistances, L L1 Lg, while C2 C1 C- 1n general it will be sufficient tomake L2w0=10r7 L1=10L, ligSlOLl, fil/052100111 and L2w0=1\2.

The principles illustrated in Fig. 9 et seq. and in Fig. 14, anddiscussed in connection therewith may be used in combination as shown inFigs. 16 and 17.

Referring to Fig. 16 as compared with 15, the .inductance L is shuntedinstead of the condenser C. Then instead of placing the valve i directlyin association with the coil L2 or condenser C2, the arrangement of Fig.10 is introduced.

Again, in Fig. 17 the coil L is sliunted (instead of the condenser C asin Fig. 14) by a secondary resonant branch L1, C1. Then a tertiaryresonant branch Lg, C2 is associated through a transformer T, and thenthetertiary condenser C2 is sliuiited by the valve i.

In the foregoing disclosure of examples of the practice of my invention,the valve has been employed to open and close the circuit of a resonantbranch comprising an inductance coil in series with a condenser. As willbe shown in connection with Fig. 26, this application of my inventionmay find utility in multiplex telegraphy. For some purposes it may bedesirable to employ filters of the recurrent section type instead ofmere resonant branches, and l will now disclose a limited number ofembodiments of my invention in connection with such filters.

Assume a low pass filter of the well known type shown in Fig. 18. For anelectromotive force applied across the terminals 109, current will betransmitted through to the terniinals 110 with substantially noattenuation for frequencies below a certain critical frequency, but forfrequencies above this critical frequency the currents will beattenuated and will get through to 110 only at greatly re ducedintensity.

Now let each shunt condenser C of this filter be shunted by a valvecombination as shown in Fig. 19 just as the condenser C of Fig. 1 issliuiited by such a combination when the switches S ai'e thrown down. Itresults that for one .lialf-cycle of the low frequency generator e1(compare Fig. 1) the filter of Fig. 19 operates just the same as thefilter Fig. 18, but for the alternate halfcycle of the generator e1 allfrequencies are blocked and the filter does not transmit any current atany frequency.

Fig. 20 shows a confluent band filter, one

which attenuates currents of frequencies below a certain criticalfrequency passes currents of frequencies between f1 and a higherfrequency and again attenuates currents of frequencies higher than f2.By shunting the series condensers C by means of valves and associatedelements as indicated in Fig. 21 (and with more detail in Fig. 1), theband filter is modified so that during one half-cycle of the lowfrequency generators associated with the valves r and r1, it operatesnormally like the filter of Fig. 20; but during the other lialf-cyele ofthese low frequency generators, the filter passes all currents offrequencies from zero up to the frequency and blocks all higherfrequencies.

It will be seen that in Fig. 22 the valves are arranged to shunt theseries iiiductances instead of the series condenseis (as in Fig. 21). InFig. 22 the filter operates normally like Fig. 20 for one half cycle onthe low frequency generators associated with the valves, but for theother half cycle the filter of Fig. 22 blocks all frequencies from zeroup to a frequency and passes all frequencies above that limit.

Fig. 23 illustrates the effect of periodically shortcircuiting certainparts of reactaiice elements of a filter. It will be noted that thevalves shown in Fig. 23 are placed in shunt respectively to parts of theinductance coils L and L,. During one half cycle of the low frequencygenerators associated with the valves of Fig. 23, the system operateslike that of Fig. 2O as a regular band filter. During the other halfcycle tlie pass band is shifted to a range whose critical frequenciesare respectively double those of thel normal range.

Fig. 24 illustrates how transformers may be used in tandem, so to speak,to get an increased ratio as compared with the single transformer ofFig. 10. This may be desirable in cases when a very great stepping downbecomes necessary on account of the relatively high resistance of thevalves einployed.

Fig. 25 shows how a plurality of Valves of which four are shown may beassociated with a single low frequency controlling source el. Betweenthe generator of the controlling source el and the valve associated inthe art I do not show them here.

with each circuit, impedance coils 105v and 106,107 and 108,109 and 110,and 111 and 112 are connected. These impedance coils present littleimpedance to the low frequency currents from the generator el, but atthehigh frequency of the signaling generators eo, elfo, suiciently highvalues to prevent currents from any one signaling circuit from iowing inany other circuit. To equalize the load on the controlling generator c1,valves r1 and r2 are so connected to allow current to flow while valvesr3 and r4 are blocking the flow of current. f

` As an application of my improved commutatorsV for multiplextransmission, I have shown a diplex telegraph system in Fig. 26. Thesingle carrier current of frequency-determined by the generator e isapplied to the line through the parallel resonant branches L, CV and L,C controlled respectively by lthe keys K and K. The coils L and L areshunted respectively bythe valves 'l' and r and the arrangement is suchthat 1 the high frequency currents from e0 are passedthrough C, Landblocked through-C', L during one half-cycle of the low frequencygenerator el and blocked through C, Land passed through C, LV during.the other halfcycle of e1. rIlhus the key K gets the line forone'half-cy cle and the keyK gets the line for the alternate half-cycle.While the frequency of the generator el is much lower than that of thegenerator e0', it is high relatively to the period of opening or closingeither key K or K.

At the receiving end the generator el will be synchronized with e0, butsince measures for accomplishing-this are old and well krolwn so, thegenerator el at the receiving end should lag in phase by a suitable timeinterval corresponding to the time of transmission over the line.

Fig. 27 illustrates a dipleX radio telephone y system. The apparatuscorresponds so closely to thatof Fig. 26 that it is thought itsstructure and mode of operation will be apparent ,without extendeddiscussion at this point.

The carrier current of frequency determined by the generator e., ismodulated by thetransmitters T and T (instead of by thekeys K and K asin Fig. 26).

In Fig. 28 I have illustrated a system for economizing frequency rangein voice transmission. Asis well known, ordinary conversation involvesfrequencies of from 100 to 2,000 cycles per second, and this range maybe deemed essential for intelligibility.

By means of the transmitter T the current due to the battery B is causedto fluctuate, and this fluctuating current through the primary of thetransformer I develops a corresponding alternating current in thesecondary circuit. This output current from the seco and cvo, theirimpedances rise to' ondary is a composite of currents ofvariousfrequencies of which those within therange from 100 to 2,000 cycles persecond are essential. 'Ihe filter F1 passes all frequencies from 100 to1,050, while thefilter F2 passes all frequencies from 1,050 to 2,000.`The output current passed by the filter F1, whose com o nents range infrequency Vfrom 100 to 1, 0, is applied in the modulator M1 to modulatea 1current of thebasic frequency `of 10,000 cycles per second.Accordingly, the output from the modulator M1 comprises the side bandsof respective frequency range from 8,950 to 9,900 and 10,000 to 11,050.These output currents go to the lter F3 which blocks the lower side bandand passes the upper side band of from 1,100 to 11,050. 'Ihe basicfrequency for the modulator M3 is 100,000 cycles per second and this ismodulated by the sideuband of frequency range from 10,100 to 11,050 sothat the' resulting side bands from thev modulator M3 have the frequencyranges respectively from/88,950 to 89,900 and 110,100 to 111,050. Again,let the filter F5 block the lower of these two side bands and pass thecurrents of frequency range from 110,100 to 111,050.

The filter F2 passes the frequency rangev filter F5 and F6 passes thesame frequencyl range, namely, from 110,100 to 111,050, a frequencywi-dthof 950 cycles, only half the frequency width of the essentialvoice range from 100 to 2,000.

Comparing Fig. 28 with Fig. 27 it will be seen that the apparatus `atthe right hand part of Fig. 28 has been obtained from Fig. 27 byomitting the` generator e., of-Fig. 27 and connecting Vthe outputcircuits4 of the filters F5 and F6 to replace the transmitters T and'Il'V ofV Fig. 27. -v i It will at once be seen that the system of Fig.`28 transmits the essential voice range on a carrier frequencyvrange of'approxi-.V

single circuit. The principle of the inven`v tion may readilybe employedto connect a larger number of branch circuits in cyclic order to asingle circuit. This is illustrated in Fig. 28a which shows a commutatorby which each of three branch circuits is connected for a third of acycle to a single circuit. The generators el, e2 and c3 are of the samefrequency and a third of a cycle apart in gahase, as shown by the fullline curves of Fig. 30. The direct current sources are so directed andof such magnitude that the axis of abscissae for the electromotiveforces on the valves 7', is brought down from O to O. Thus each valve 1passes current from c1 or e2 or e3 for two thirds of a cycle and blocksit for one third of a cycle, and accorlingly, each resonant branch L, Cpasses current for one third of a cycle, and blocks it for two thirds ofa cycle.

lVhen two step valves are employed, such as those of Fig. 14, thearrangement must be as in Fig. 29; that is the sources V must bereversed as compared with Fig. 28a and Fig. 30.

When three step valves are employed as in Fig. 15, or any odd number ofsteps, the diagram of Fig. 30 is applicable. For any even number ofsteps the diagram of Fig. 29 applies.

For quadruplex operation, each transmission period should be a quartercycle. In this case only two control sources are required, El sin wland-E1 cos w12?. These may take the place of e1 in each of two systemslike that of Fig. 8 or Fig. 11, the phase relations being shown in Fig.32. In case two (or four) step valve circuits are employed, the properdiagram is given in Fig. 31 instead of Fig. 32.

I claim:

1. An interrupter for an alternating current of a certain frequencycomprising a branch circuit resonant to that frequency, a valve shuntingan element of said branch, and a local source of electromotive forceassociated with said valve.

2. The method of commuta-ting a relatively high frequency alternatingcurrent through a. resonant branch circuit having a valve in shunt to anelement thereof which consists in applying a relatively low frequencylocal electromotive force to the valve and thereby blocking the highfrequency current for part of each cycle of the low frequency force andpassing it for another part thereof.

3. In combination, an inductance coil and a condenser in series, a shuntnetwork around one of these elements, a valve comprised in said network,and means to vary the resistance of the valve cyclically and thereby toproduce a corresponding wide change in the impedance at the resonantfrequency across the terminals of said inductance and condenser inseries.

4. In combination, an induct-ance coil and a condenser in series, ashunt network around one of these elements, a two electrode thermionicvacuum tube comprised in said network, an alternating current generatorin shunt to said tube, said generator being of low7 frequency comparedto the resonant frequency of said coil and condenser, an inductance inseries with said generator and having high impedance to said resonantfrequency but low to said generator frequency, and a direct currentsource also in series with said generator. A

5. In combination, a plurality of resonant branch circuits of the samenatural frequency connected in multiple to a single circuit, and meansto make the connections effective at that frequency for one branch andineffective for the others in cyclic order, said means comprisingnetworks each in shunt to one element of a respective branch, eachnetwork comprising a valve and a local source of direct current and alocal source of alternatingl current applied to said valve, saidalternating current sources being at different phases but on the samefrequency, and said frequency being low compared to said naturalfrequency.

6. Means to interrupt regularly a current of a certain frequency througha coil and con-- denser in series resonant to that frequency, whichcomprises a valve in shunt to one of said elements and a localalternating current source applied to said valve, said source being ofrelatively lovs7 frequency.

In testimony whereof, I have signed my name to this specification this11th day of December 1929.

JOI-IN STONE STONE.

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